Okay there is nothing to worry about.  
Since it is a misdemeanor and not a felony the charges or fines are minimal. 

I am pretty sure that you have got a arraignment date for the case.  On that day the judge will ask you either to plead guilty, plead not guilty or No contest.  In pleading guilty your friend will be out by paying a minimal amount of state fine for selling of alcoholic beverage to minor.  If you "plead not guilty" you will go to trial with a attorney on your defense.  On that case the state attorney will prepare a case against you friend and try to find as much information as possible.  It might be possible that they might pull a thread about immigration and everything comes out from selling alcohol and immigration.  The last one is "No Contest" in which your friend will accept the misdemeanor but hasn't plead gulilty yet. This case comes when you are arrested and released on a bond and you give a statement to the police. 
So the best move will be to plead guilty and to pay the fine and leave it quietly.  Because if you go to trial your criminal/background check will be done. But if the case doesn't goes beyond arraignment, there will be no background check and no trial.
Be careful the next time.
Anymore questions, let me know..